This project is for gaining an understanding of how the virus of equine infectious anemia (EIAV) is able to infect horse, successfully elude the host defenses for life, and cause periodic, recurrent clinical disease. The ability of this RNA virus to make a DNA copy of its genome and insert it into the host's chromosomes may be the key to its evasion of the immune response. This project will examine the details of the interaction of EIAV with various types of cells of both equine and non-equine origin to define how the virus functions. The kinetics of various events in the cell following infection will be followed. The functioning of the DNA provirus will be studied by nucleic acid hybridization techniques. The type of cell in the horse which is persistently infected will be identified by similar techniques. Whether or not the virus undergoes antigenic modulation in vivo will be determined, and attempts will be made to mimic this phenomenon in vitro with a model system. The response of the cell-mediated immune system to EIAV-infected cells will be defined and attempts will be made to induce resistance to disease by stimulation of this response. Lastly, the viral antigens and corresponding anti-viral antibodies that are responsible for the immunologically-mediated red blood cell destruction will be identified.